Biliary lipid metabolism was investigated in a series of 6 subjects and a comparison was made between these kinetics in the fasting state and in the fed state. After ingesting a normal diet the patients had gallbladder bile sampled and biliary lipid turnover studies performed. The subjects were then fasted for a period of 5 to 6 days. After the 4th day of fasting, biliary lipid parameters were again determined. The results in this study include the following: 1) total bile acid pool and cholic acid pool were either slightly reduced or unchanged by fasting, both cholic acid synthesis and the fractional catabolic rate of cholic acid was reduced during the fasting state. Gallbladder bile was rendered less lithogenic during the fasting state compared to the fed state. There were no changes in bile acid composition either in the fed or fasting state.